1. Field of the Invention
The present invention relates to a method for manufacturing a surface mount type semiconductor device with leadless structure. In particular, this invention relates to a method for manufacturing a thin semiconductor device with low-cost. This invention also relates to an adhesive sheet for use in such a method for manufacturing a semiconductor device. This invention further relates to a surface mount type semiconductor device with leadless structure, which is thin and with low-cost.
2. Description of the Related Art
Packages of individual components such as semiconductor integrated circuits, transistors, and diodes have been made smaller and thinner. In the field of semiconductor integrated circuits with lead frames, there has been a demand for a finer lead pitch of the lead frames for the purpose of forming a larger number of pins. If the lead width is reduced to meet such a demand, however, the strength of the lead is reduced so that the lead can bend to form a short circuit. A certain lead pitch should also be fixed, and therefore the packages should have a relatively large size. Thus, the packages with the lead frame have been relatively large in size and relatively thick. For the purpose of excluding the influence of the lead frame, therefore, surface mount type semiconductor devices with leadless structure have been proposed.
Japanese Patent Laid-Open No. 9-252014 (1997) discloses an example of the leadless semiconductor device as shown in FIG. 9. The method for manufacturing such a semiconductor device includes the steps of attaching a metal foil to a base member 3; etching the metal foil so as to leave certain portions thereof; using an adhesive 2 to fix a semiconductor element 1 to a metal foil portion (die pad) 4a, which is substantially the same in size as the semiconductor element 1; electrically connecting wires 6 between the semiconductor element 1 and metal foil portions 4b; performing transfer molding with a sealing resin 5 in dies; and finally separating the molded sealing resin from the base member 3 to form a packaged semiconductor element. However, the semiconductor device produced by this method includes the adhesive 2 and the metal foil portion (die pad) 4a associated with the semiconductor element 1. Such a structure may still have a problem in satisfying the demand for small thin semiconductor devices in the industrial field.
In the process disclosed in the publication, the base member 3 has to sufficiently adhere to the metal foil portions 4a and 4b during the step of etching the metal foil and the step of transfer molding with the sealing resin. After the transfer molding step, on the other hand, the base member 3 has to be easily detached from the molded resin 5 and from the metal foil portions 4a and 4b. Thus, contrary properties are required about the contact between the base member 3 and the metal foil portions 4a and 4b. Specifically, the adhesion is required to be durable to etching chemicals and to be so durable as not to allow the semiconductor element 1 to shift at high temperature under a pressure applied by the mold resin running in the dies in the transfer molding step. In contrast, after the resin molding, the base member 3 must easily be separated from the molded resin 5 and from the metal foil portions 4a and 4b. However, the material of the base member 3 such as a fluoropolymer, silicone, and a fluoro-coated metal as disclosed in the publication can never satisfy the above contrary requirements for the contact.
Japanese Patent Laid-Open No. 2001-210743 discloses another example of the leadless semiconductor device and a manufacturing process thereof. FIG. 10 shows one of the semiconductor devices as disclosed in this publication. Such a semiconductor device is fabricated as follows. A metal plate 4 with a matrix of grooves x is prepared as a base member. A semiconductor element 1 is fixed to the metal plate 4 using an adhesive 2. Wires 6 are provided by wire bonding at designed necessary portions and then sealed in a sealing resin 5 (FIG. 10 at (a)). The metal plate 4 and the adhesive 2 are then ground, and the sealing resin 5 and the metal plate 4 are cut in a designed size to form a semiconductor device (FIG. 10 at (b)). However, the semiconductor device produced by this process also includes the adhesive layer 2 and the metal plate 4y coexisting under the semiconductor element 1. Such a structure may still have a problem in satisfying the demand for thin semiconductor devices in the industrial field.
As described above, the conventional manufacturing process has difficulty in achieving thinner semiconductor devices. In the conventional process, therefore, the semiconductor element itself should be ground into a thin form in order to form a thin semiconductor device. In such a process, therefore, cracking or chipping may often occur in chips, which can cause to increase in cost. The use of the adhesive and the like also involves additional steps and materials, which can also cause to increase in cost.
It is an object of the present invention to provide a manufacturing process that can produce a surface mount type semiconductor device with leadless structure, in a thinner form.
It is another object of this invention to provide an adhesive sheet useful for such a manufacturing process.
It is yet another object of this invention to provide a surface mount type semiconductor device with leadless structure, in a thin form.